assad regime forces are suffering real military setbacks means that now assad is preparing his last defense against the opposition overthrowing him. >> greta: well, the shelf life as we understand of sarin gas is 60 days. now that it's mixed, there's a 60-day window. of course, that doesn't mean if he does act that he won't act within the next 20 seconds. we have no way of knowing. i'm curious. how far can his missiles reach out of syria? is he likely -- i mean, should other nations in the area be concerned? >> well, i think by definition this is very dangerous stuff, and it's unstable, mads obviously to being highly toxic. it's dangerous for anybody to be around. one of the problems with chemical weapons has always been how you deliver them. the explosive force of normal ar tillery or missile destroys the chemical weapons. being able to actually use it effectively has been a military problem. i don't think that it's likely assad would use this across the turnish border, for example. i think it's far more likely he's threatening the opposition and basically either for negotiating purposes o